Introduction. 



The close examination of the Hydrocorallines meets perhaps with more difficulties than the 

 study of the skeleton-bearing Hexacorallia, owing partly to the porous skeleton of the colonies, 

 partly to the delicate nature of the organisms. The characteristics can be determined roughly by 

 means of Dr. Koch's detailed method in which thin sections of the colonies are prepared by grinding 

 with the stained soft parts in situ. The structure of the skeleton can also in part be studied by 

 breaking the colonies as Hickson (1912 p. 891) seems from the following remark to have done. "The 

 way in which it is possible to study the shape of the gasteropore styles is to make a vertical fracture 

 in a plane parallel with the long axis of a branch. In a large percentage of such fractures the whole 

 length of at least one gasteropore with its style will be exposed". It is evident however, that this 

 method is not suited to form the base of a more thorough and systematic investigation of the skeletal 

 parts of the colony. Where it is necessary for the observer to make his results free from chance 

 irregularities he must have recourse to the somewhat slower method of grinding. In the present 

 studies this latter method has throughout been used in the examination of the skeleton. The soft 

 parts are first removed by means of Eau-de-L,abarraque, and pieces of the colony have then been 

 ground down on a fine and level whetstone as far as seemed necessary in each single case. For 

 general systematic work it is usually sufficient to grind down a branch to about its median longi- 

 tudinal plane; in a Stylaster, for example, the majority of the gasterostyles will in most cases 

 appear quite free in the middle of the gasteropore. On the finely polished ground surface it will also 

 be possible to study the course of the fine canals. Where there is question of examining the finer 

 structure of the calcareous skeleton, however, this procedure is not sufficient and it is necessary in 

 addition to have thin sections of the same kind as the geologists use in their studies. 



Since Moseley's fundamental work on the Hydrocorallines appeared in 1881 investigators have 

 mainly directed their attention towards unravelling the features of the skeleton of the colonies. Ex- 

 cluding a couple of smaller papers on the gonophores of a few species, no observer since that time 

 has sought to penetrate deeper into the organisation and finer structure of the Hydrocorallines. The 

 result is, that we cannot yet be said to have full knowledge of their affinities and thus of their syste- 

 matic position, a matter I shall return to later. On studying Moseley's work we see at once, that 

 none of the species hitherto found in the northern seas have been closely investigated; as will 

 be shown in the following; even their specific characters have been more or less imperfectly 



The Ingolf-Expedition. V. 5. I 



